This application targets the development of immunotherapy against diarrhea-associated hemolytic uremic syndrome (D+HUS). This disease is caused by Shiga toxin-producing E. coli (STEC), primarily the O157:H7 serotype. These bacteria are virulent Category B pathogens, associated primarily with food and waterborne acquired disease with relevance to potential bioterrorism. D+HUS is a life-threatening illness in children and the elderly that is heralded by the sudden onset of pallor and oliguria. The acute mortality rate remains 3-5% and nearly 25% of patients develop serious extra-renal complications. There is no treatment for D+HUS that ameliorates the disease course or reduces the need for acute dialysis support. Because D+HUS is an orphan disease, federal funding is urgently required to facilitate the development of effective therapeutic agents. There are no current NIH-funded clinical trials to assess novel treatments for D+HUS. Our team has developed and characterized a panel of neutralizing human monoclonal antibodies (Hu-MAb) which are highly active in vitro and in vivo against Shiga toxins 1 and 2. These antibodies have undergone extensive preclinical evaluation in an appropriate animal model. This application is designed to test the hypothesis that administration of a Hu-MAb to Stx2 will: (1) be safely tolerated by healthy adult volunteers and a test cohort of children with STEC enteritis and D+HUS; and (2) ameliorate the clinical severity and disease course in patients with D+HUS. The Specific Aims of this application are: (1) Manufacture of Phase I GMP clinical material, namely a Hu-MAb to Stx2, for use in Phase I and II clinical trials, confirm efficacy in an experimental model, and file an IND application (Interval 1); (2) Performance of a comprehensive Phase I placebo-controlled, dose escalation and pharmacokinetic study of Hu-MAb to Stx2 in healthy adult volunteers and in a sample cohort of children with STEC enteritis and D+HUS (Interval 2); and (3) Performance of a Phase II study of Hu-MAb to Stx2 in children with D+HUS (amelioration) (Interval 3). The significance of this application is that it may facilitate the development of a safe and effective immunotherapeutic biological product that can be given to individuals exposed to an accidental or deliberate (bioterrorism) STEC contamination of food or water sources.